A) Field of the Invention
The present invention relates to a communication system having dominating nodes and dominated nodes, and more particularly to a dominating node capable of managing other nodes and a dominated node to be dominated by the dominating node.
B) Description of the Related Art
IEEE1394 is known as the standards of a serial interface capable of large capacity high speed data transfer. An interface complied with the IEEE1394 standards and an apparatus having this interface (hereinafter collectively called an IEEE1394 device) constitute one node having hardware IEEE1394 bus protocols (lower layer) and software protocols (upper layer) for device control, isochronous transmission control and the like.
FIG. 9 is a conceptual diagram showing an example of a protocol stack of a general audio visual (AV) apparatus having an mLAN (trademark) upper layer. The mLAN standards are complied with the IEEE1394 standards and are an application at a higher level than the IEEE1394 standards, constituting a digital network system for music.
The lower layer is constituted of, for example, a physical layer, a link layer, a transaction layer, and a serial bus management layer.
The physical layer defines physical and electrical interfaces. The physical layer is generally made of hardware.
The link layer provides one-way transmission service called sub-action and packet transmission/reception service (packet handler). Similar to the physical layer, the link layer is also generally made of hardware. The link layer provides, for example, synchronous transmission and isochronous transmission services.
Isochronous transmission is used for signals requiring high speed processing such as audio signals and video signals. The link layer of hardware provides all services of the isochronous transmission.
The transaction layer deals with synchronous transmission. The transaction is a data transmission of a request-response type. There are three transaction types, a read transaction, a write transaction and a lock transaction.
The read transaction is used for reading data from a specific target address space. The write transaction is used for writing data in a specific target address space. The lock transaction is used for renewing data in a specific target address space in accordance with reference data.
The serial bus management layer is a module for concentrically managing resources on the bus. The bus management includes management of power supplies, management of a topology map and a speed map, management of isochronous resources, and the like.
The upper layer is software for managing the lower layer and the whole node, and is constituted of, for example, the 1394AV protocols (IEC-61883) and mLAN upper layer.
The 1394AV protocols define a common isochronous packet (CIP) format for expressing the data contents of an isochronous packet, a connection management protocol (CMP) for managing connections by defining a virtual “plug”, a function control protocol (FCP) for managing other devices connected to the IEEE1394 bus, and the like.
The mLAN upper layer is a protocol layer for transmission of audio/music information in accordance with the IEEE1394 standards. The mLAN upper layer is constituted of an audio/music information transmission protocol and a connection management protocol both complied with the 1394AV protocols.
The audio/music information transmission protocol is used for adding the format for transmitting audio/music information to the definition of CIP. The connection management protocol is used for performing autonomous connection management of each node by using an intelligent CMP.
All IEEE1394 devices connected to an IEEE1394 bus have the upper and lower layers although the functions thereof are different more or less.
The upper layer is more complicated than the lower layer. Therefore, hardware resources necessary for the upper layer increase more than the lower layer. The manufacture cost rises if the upper layer is used for all IEEE1394 devices.
The upper layer is more relevant to a user interface than the lower layer. There are, therefore, many chances of feeding back revision requests from users. Although it is desired that the upper layer has the structure easy to match a new specification, the manufacture cost rises if the structure of the upper layer of each of all IEEE1394 devices is made easy to upgrade.